In existing wireless technologies, signal repeating devices, or “repeaters” are used to extend the coverage of the overall wireless system beyond traditional base stations. For example, an overall wireless system may consist of a plurality of base stations that communicate with each other and operate to provide a defined coverage area. In such coverage areas, there are often smaller geographical areas that have very low signal reception with respect to one or more of the base stations. For example, such areas of low signal coverage may be within buildings or areas that are otherwise obstructed. Rather than implementing another costly and large base station to provide coverage to such low signal areas, repeaters are utilized.
A repeater essentially has a donor antenna that is in communication with one or more base stations. The repeater receives downlink signals from the base station, processes and amplifies those signals, and then re-transmits or “repeats” those signals through a coverage antenna into the area that otherwise has low signal reception or low signal power. Signals from mobile devices, such as wireless phones or other equipment, send any uplink signals back to the repeater, and that uplink traffic is repeated back to a base station.
For example, referring to FIG. 1, a basic wireless communication system 10 might include a base station 12 that communicates with a repeater system 14 having a donor antenna 16, a coverage antenna 18, and processing electronics 20 that are positioned between the antennas 16 and 18 to process and amplify the repeated signal. Accordingly, downlink wireless signals 22 are received by the donor antenna 16 of the repeater, and are then amplified and repeated through the coverage antenna 18 as downlink signals 22a. The downlink signals 22a are received by one or more wireless communication devices, such as mobile phones 24. Similarly, in an uplink direction, as indicated by reference numerals 26 and 26a, the wireless device 24 communicates signals 26a back to the coverage antenna and the repeated signal 26 is then provided as an uplink signal back to the base station 12. As would be readily understood by a person of ordinary skill in the art, such repeater systems 14 can take many different forms and are not limited only to devices conventionally called “repeaters”.
Some repeater systems provide frequency translation in the repeated signals such that signals received from the base station by the repeater are then transmitted at a different frequency to the mobile devices or other wireless devices. In such a scenario, signal isolation between the antennas and the problems with feedback from the transmitter coverage antenna to the receiver or donor antenna is not a problem because the signals handled by those different antennas are at different frequencies, allowing the feedback signal to be attenuated with a frequency selective filter. However, in a non-translating repeater, the isolation between the two opposing antennas or sets of antennas can limit the performance of the repeater.
If there is insufficient attenuation or isolation between the transmit side output and the receive side input, then the repeater can oscillate due to the feedback signals. This causes significant performance problems. To ensure stability, it is generally desirable to provide gain or amplification in the repeater that is less than the isolation between the antennas. Generally, a repeater will be configured and operated to maintain a certain gain margin to determine how close it is to operating in an oscillatory or unstable condition. If the gain margin is too small, then the repeater's gain might be reduced or attenuated until the gain margin is above an acceptable threshold.
Generally, when a repeater is installed or commissioned, the antenna isolation between the receive and transmit antennas can be measured, and the gain margin for the repeater might be estimated by calculating the gain margin as being the (antenna isolation) minus (repeater gain). However, while such a gain margin determination and gain setting may be sufficient at initial installation, such an installation methodology for providing stability in a repeater is not adaptive. That is, the initial settings and gain margin do not take into account or accommodate any changes in the antenna isolation or any changes in the gain of the repeater. Accordingly, it is desirable to periodically or continuously measure gain margin during normal repeater operation, and to then make the necessary adjustments to the repeater's gain to ensure stability.
During normal repeater operations, both the input signal (that is, the signal to be amplified and re-transmitted) and the feedback signal (that is, the unwanted signal that is fed back from the transmit antenna) are combined into one receive signal at the receive antenna. To measure the gain margin, the level of each signal needs to be determined separately. However, in a non-translating repeater, a problem with separating the signals arises because the input signal and the feedback signal are essentially the same signal with the same frequency. The feedback signal is slightly delayed in time.
One possible way to separate the input feedback signal would be to momentarily connect the repeated transmitter to a test signal, and then measure the level of the test signal at the receive input of the repeater. Measuring the test signal in the presence of the input signal may be utilized to determine the repeater's antenna isolation and gain margin. However, during such a solution, the input repeater signal is not transmitted during the time of the test signal. This causes a momentary and undesirable interruption of the service of the repeater. For example, it might lead to dropped calls or other service interruptions in the coverage area of the repeater.
Accordingly, it is desirable to provide a repeater that has adaptive gain margin measurements and adjustment while continuing uninterrupted service.